This invention relates generally to devices that are used to make an arcuate cut through a solid substance, and more particularly to devices used to make an arcuate cut through a bone as part of an osteotomy procedure.
An osteotomy is a surgical procedure used to correct a defective bone orientation. To perform the procedure, the defectively oriented bone is severed into two matable sections, and then these sections are reoriented.
There are various types of osteotomies in which arcuate cuts are made in a bone's entire cross section. For example, in a high femoral or inter-trochanteric osteotomies, an arcuate cut is made in the entire cross section of a living subject's femur. Additionally, according to the teaching in U.S. Pat. No. 4,409,973 to Neufeld, an arcuate cut is made in the entire cross section of the subject's tibia.
Another type of osteotomy involves making an arcuate cut in only a portion of the cross section of the subject's bone. For example, as taught in U.S. Pat. No. 4,677,973 to Slocum, an arcuate cut is made in only a portion of the canine tibia, i.e. the metaphyseal region of the tibia.
In each of the above-identified osteotomies, the arcuate-cut procedure is very important, and critical to success. A key aspect of the arcuate-cut procedure is the quality of the "match" between mating surfaces formed by the cut. The better the "match", the better the bone will be supported when the surfaces are rejoined and the osteotomy is completed.
When an arcuate cut is made, it is made in a curvilinear plane through the bone, or bone portion, as in the tibial portion that is cut in the proximal tibial osteotomy disclosed in U.S. Pat. No. 4,677,973 to Slocum. Such a cut divides the bone into two mating-bone sections having corresponding mating surfaces. A key feature of the two surfaces is the radius of curvature that defines them.
In theory, the "perfect" cut would produce two mating-bone sections whose mating surfaces "match" perfectly, i.e. the two surfaces mating at an infinite number of lines in the curvilinear plane in which the cut was made. Such a perfect "match" is possible only if the two surfaces have identical radii of curvature.
Because the two surfaces' curvature radii are defined by the cylindrical saw's mating-surface-forming blade, the saw blade is an important element in the success of an osteotomy. Such a blade includes an outer cylindrical surface defined by one radius of curvature and an inner cylindrical surface defined by another radius of curvature.
Conventional cylindrical saws used in performing osteotomies are not capable of making the "perfect" cut because their saw blades have outer and inner cylindrical surfaces that are defined by different curvature radii.
An example of such a prior-art saw blade is shown in U.S. Pat. No. 4,409,973 to Neufeld. Neufeld discloses a cylindrical saw having an elongate, semi-cylindrical saw blade. The saw blade includes an outer and inner semi-cylindrical surface, the outer surface of which has a radius of curvature greater than the blade's inner surface.
Because the saw blade's surfaces have different curvature radii, mating-bone surfaces formed by the blade will only marginally mate. This is so because the mating-bone surfaces will have different curvature radii, one defined by the saw blade's outer surface and the other defined by the saw blade's inner surface.
It is therefore an object of the present invention to provide an arcuate saw blade for making an arcuate cut through a solid substance that greatly improves the conformity of the substance's cut-produced, mating surfaces.
A further object of the present invention is to provide an arcuate saw blade for use in corrective osteotomies that produces two bone sections having mating surfaces that more 10 perfectly "match", thus providing greatly increased stability to the rejoined bone sections.
A still further object of the invention so far outlined is to provide an arcuate saw blade usable to make an arcuate cut that facilitates fixation of the cut-produced, mating-bone sections relative to each other.
Yet another object of the present invention is to provide an arcuate saw blade for use in corrective osteotomies that will promote healing of the rejoined bone sections by providing an improved "match" between the bone sections' corresponding mating surfaces.
The invention described herein achieves the above-identified objects by providing a biradial saw including a biradial saw blade having an elongate, arcuate body. The body includes a cutting end, and inner and outer arcuate surfaces, each being characterized by substantially the same radius of curvature. However, the body's surfaces have different axes of curvature.
To make a desired cut in a solid substance such as a bone, the blade is oscillated about a cutting axis in the curvilinear planes of its surfaces. The cutting axis substantially parallels the surfaces axes of curvature and is located between them.
As the blade moves through the bone, it cuts the same into two sections having matable, cut-produced surfaces that more nearly have the same radii of curvature.
Because the saw blade's inner and outer surfaces have different axes of curvature, minor "shaving" of bone, or other material, will occur because, during the cutting operation, both surfaces are oscillated about the same cutting axis. The term shaving refers to an action that occurs when the cutting axis is in an off-axis position relative to either curvature axis of the blade's inner or outer surface.
To take maximum advantage of the saw of the invention, the cutting axis is offset from the inner and outer surfaces' axes of curvature. In the preferred embodiment, the cutting axis is located at an optimum offset which is substantially halfway between the surfaces' axes of curvature.
Also, to further maximize the advantage of the invention, the saw blade is oscillated through an angle of 5.degree.-15.degree..
These and other advantages and objectives of the present invention will become more fully apparent as the description which follows is read in conjunction with accompanying drawings.